Vinyl ester resins and unsaturated polyesters are known resinous materials finding widespread use in a variety of applications, such as coatings, laminates, moldings, encapsulants, etc. The resins may be employed in filled or unfilled formulations with or without colorants and other additives and with or without reinforcing elements, such as glass or carbon fibers.
Those vinyl ester resins are essentially the product of the reaction of a polyepoxide with an unsaturated monocarboxylic acid to result in a molecule having terminal olefinic unsaturation. The resins alone or with a reactive diluent are polymerized by the addition polymerization of that terminal unsaturation using free radical catalysis techniques. Among the catalysts finding common usage for curing the resins are the various peroxides. Equally common is the use of organometallic promoters with those peroxides. With some combinations of such promoters and peroxides, a gas, essentially oxygen, is generated during the curing process of vinyl ester resins. That gas is entrapped in the resin system leaving the product unattractive and also adversely affecting the properties of the cured product. The problem is manifested particularly with those catalysts that are prepared with hydrogen peroxide which frequently have some residual H.sub.2 O.sub.2. Also, the problem can occur with those peroxides that generate H.sub.2 O.sub.2 in a given catalytic combination. The problem is most acute with cobalt salts since they are supplied as a four coordinated compound leaving two potential coordination sites to react with any hydrogen peroxide to produce oxygen.
The problem is not as evident with unsaturated polyesters presumably because maleic acid is a common diacid used in making such resins. Residual maleic acid may be suppressing the foam. That phenomenon is noted in Belgian Pat. No. 817,001.